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In email marketing, the term bounce is used for any email which returns an error because the email did not make it to the recipient. Subsequently, the terms hard bounce and soft bounce are commonly used and it is generally accepted that a hard bounce represents a permanent failure, whereas a soft bounce shows a failure that could be temporary.
As a result, it makes sense to immediately remove all hard bounce email addresses from your mailing lists and monitor the soft bounce addresses to remove them if the soft bounces continue. ClickDimensions does this automatically through a feature we call Service Protection.
Service Protection Bounce Logic
Bounces, both soft and hard, can negatively impact your sending reputation. While bounces are a part of email marketing, you still want to keep them under 5%. Sustained high bounce rates are indicative of an authentication or list quality issue that needs to be addressed. As a sender, if you have a high bounce rate or continue to send to email addresses that bounced previously, your sending reputation lowers. ClickDimensions uses Service Protection to exclude invalid email addresses from future email sends and protect your sending reputation.
We do not automatically remove bounced recipients from user's marketing lists. We do exclude any listed recipients from being sent to if previous attempts to email them resulted in one of the following.
- 1 Hard Bounce
- 4 Soft Bounces in a 90-day period
- Soft Bounces that are the result of an IP or Domain being blocklisted or a Spam Block will not count toward the 4 soft bounces in 90 days
NOTE: Most emails will have a delivery or bounce status immediately after the send completes. Some soft bounces will take up to 72 hours to resolve, so if an email has a transient soft bounce, ClickDimensions will retry the email at a regular cadence for up to 72 hours. If the email doesn’t successfully deliver after 72 hours, it will have a soft bounce status. You may see the delivery and bounce metrics change up to 3 days after the send.
Bounce Categories
Soft Bounces
Soft Bounces are considered the result of a temporary or fixable issue. Although it can be indicative of an issue that will turn permanent which is why if an email continues to soft bounce we will exclude it. Soft Bounces can use an SMTP Code that starts with 4 (SMTP;4xx) or with 5 (SMTP;5xx) and will usually include a human-readable description of the reason for the bounce.
Common reasons why an email will Soft Bounce
| Bounce Category | Definition | Email Event Bounce Type |
|---|---|---|
| Inactive Account | Email address is temporarily disabled or unavailable | Soft Bounce |
| Mailbox Full | Recipient’s mailbox has exceeded the storage allocation | Soft Bounce |
| Administrative Mail Block | Recipient has set up a rule to not accept email from a particular sender | Soft Bounce |
| Content Mail Block | Recipient has identified your email as likely spam due to content | Soft Bounce |
| Policy Mail Block | Recipient is blocking mail because of an authentication failure | Soft Bounce |
| IP or Domain Blocklisting | The sending IP or domain is temporarily blocklisted | Soft Bounce |
| Spam Block | Recipient may have blocklisted the sending IP or domain, and in some cases bounces may be caused by a content block or authentication failure. Bounces in this category will not count toward the 4 bounces in 90 days | Soft Bounce |
| Invalid Email Syntax | Recipient email address has improper syntax | Soft Bounce |
| Domain Suppression | Domain is on our suppression list of commonly misspelled domains | Soft Bounce |
| Timeout | Email job has exceeded the 24 hour time limit to be processed | Soft Bounce |
| Generic Bounce | Can be a number of issues including authentication issues, email content, too many hops, temporary technical issue on recipient side | Soft Bounce |
| Undetermined | Can be a number of issues including message too large, hop count exceeded, inactive account, etc. | Soft Bounce |
Hard bounces
Hard Bounces are considered permanent failures and usually the cause of an invalid recipient email address.
Common reasons why an email will Hard Bounce
| Bounce Category | Definition | Email Event Bounce Type |
|---|---|---|
| Invalid Recipient | Recipient email address is invalid; Usually domain exists but there is not an account for that recipient | Invalid Recipient |
| DNS Failure | Domain used in recipient email address either doesn’t exist or does not have MX records | DNS Failure |
Spam Complaints
Spam Complaints are not technically bounces—since the email is being delivered—but they are handled similar to a bounce event. When a recipient marks an email as spam and the email provider has a feedback loop available, we will take the spam complaint response and exclude the email address from future sends.
| Bounce Category | Definition | Email Event Bounce Type |
|---|---|---|
| Spam Complaint | Recipient marks email as spam | Spam Content |
Bounce Events
When looking at bounce Email Events via Advanced Find or in the individual Email Event records, the only Bounce Types that will be displayed are Soft Bounce, Invalid Recipient, DNS Failure, and Spam Content. While there are many reasons why an email may Soft Bounce, they will all be displayed under the Soft Bounce Email Event Type. You’ll need to look at the Email Event Message for more information.
SMTP Codes and Bounce Messages
While the general rule is that Soft Bounces are temporary issues, and that Hard Bounces are permanent, the reality is that every mail server is configured differently and there are no hard rules; the power to decide whether an email message is received, and the reason given (if any) for a bounce belongs 100% to the recipient. We have seen invalid email addresses come back with a soft bounce SMTP category and temporary issues returned with a hard bounce SMTP category. Two different email servers will often use the same code and category in completely different ways. However, we do our best to filter the responses based on category and message.
FAQs
I see some Soft Bounces that don’t have a message—is that an error?
No, there are some bounces in the Generic Bounce and Undetermined category that don’t include a message. The messages sent back are configured by the individual email servers and they may choose to not send a message back with the bounce. Because ClickDimensions receives bounce information from the receiving mail server and syncs it to an Email Event, if no bounce message was included then we do not have a message to display.
We have a recipient address that was blocked due to soft bounces but we’ve been able to resolve the issue causing the bounce. Can we unblock the email address?
Yes. If you are on version 8.10+ of ClickDimensions, you have the ability to unblock individual email addresses.
I have recipients that have both a bounce and a deliver event. What is happening?
Some email servers will initially accept an email (send back a delivery acknowledgement) then later bounce the email back (send a bounce message) perhaps because the domain is correct, but the individual account does not exist. ClickDimensions will intake all server responses and sync those to CRM as email events.
What is considered a normal bounce rate?
The ideal bounce rate is under 5%. Anything over 10% would be considered a red flag and need to be investigated.
Are all Soft Bounces counted toward the 4 in 90 days that result in excluded emails?
No. Bounces that are in the Spam Block category will not count toward the 4 bounces in 90 days. Bounces that fall into the Spam Block category include bounces from an IP or domain being blocklisted, and in some cases bounces from a content block or authentication failure. Sometimes it will depend on how the recipient server is categorizing the bounce.
We have bounces that say, “hop count exceeded,” what does that mean?
Sometimes you’ll see bounces that look like this . . .
smtp;554 5.4.14 Hop count exceeded - possible mail loop
Every time an email is passes between servers a hop is recorded in the headers. Typically, there are 2–4 hops before an email reaches its destination. If the receiving email server is configured incorrectly where the email is passed to too many servers or it gets into an endless loop, the server will bounce it back. This is an issue with the receiving email server.
What does it mean when an email is rejected due to a DMARC policy?
If your sending domain is configured with DMARC, you’ll need to customize your ClickDimensions email account. See our help article about Using DMARC with ClickDimensions Email.
Are there any resources to research the meaning of bounces codes and messages?
Yes. Below are some helpful bounce code reference sites.